The prevalence of obesity and insulin (INS) resistance in adult Pima Indians (PI) is high. Increased adipocyte (AC) size and increased INS resistance are both associated with obesity in PI and Caucasians (CA). We wished to determine whether AC size and INS resistance are increased in age and obesity matched lean PI children relative to lean CA children. We estimated abdominal and gluteal AC sizes and fasting and post prandial plasma glucose and INS concentrations during a 3 hr OGTT in lean (percent body fat less than 20%) prepubertal PI and CA children and gluteal AC size were similar in PI and CA, respectively. Abdominal AC size, fasting [INS], INS area above fasting and fasting [glucose] were higher in PI than CA children. Thus, relative to lean CA children, lean PI children have increased abdominal AC size, increased fasting and postprandial INS concentrations and increased fasting glucose concentrations, which are findings typically seen in obesity. Thus, it appears that these changes are not necessarily due to obesity and may be predictors for obesity. The Epidemiology Section has shown that children of women who were diabetic before and during pregnancy (DIA) had greatly increased mean weight for age and height than both children of women who were non-diabetic during pregnancy but developed NIDDM Later in life (NDP), and children of women who never developed diabetes and came from families with a low prevalence of NIDDM (LPN). To determine whether differences exist between the 3 groups of children that might (be related to increased growth and a possible change in body composition in DIA) have estimated obesity, abdominal and gluteal ACS and fasting and stimulated glucose and INS levels during a 3 hr OGTT in prepubertal 7-11 year old children, with a range of obesity from 6-40% body fat, from these 3 groups. Age, body mass index, (weight/height2) % ideal weight and obesity (% body fat) were similar in DIA (n=17), NDP (n=13) and LPN (n=7), respectively. Body composition was thus similar. There were no differences in and/or AC or in fasting stimulated glucose and INS levels, between the groups. This suggests that the pattern of excess growth in DIA is the same as that of simple obesity, and is different from that which leads to excess fat of infants with diabetic microsomia.